Fabrication of two-dimensionally arrayed quantum device

ABSTRACT

A quantum device is constituted from a two-dimensional array of quantum dots formed from metal atom aggregates contained in metalloprotein complex. The metalloprotein is arranged on the surface of a substrate having an insulation layer with a pitch of the size of the metalloprotein complex. The diameter of the metal atom aggregates used in the quantum device is 7 nm or smaller, and the pitch of the metalloprotein complex is preferably from 11 to 14 nm.

This application is a divisional of Ser. No. 09/086,672, filed May 29,1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a quantum device wherein quantum dotsare arrayed in two-dimensional configuration. The quantum dots arrayedon the quantum device can be preferably used as single-electrontransistor, doping diode, doping transistor, doping transistor array andsemiconductor light emitting device.

2. Description of Related Art

Devices that utilize single-electron tunnel effect such assingle-electron transistor and single-electron memory are attractingmuch attention. The single-electron transistor, for example, is apromising candidate that can replace MOSFETs to satisfy the requirementsof miniaturization of devices to the order of sub-micron for whichimprovements on the MOSFETs, the mainstream technology in the field ofsemiconductor transistor, are reaching limitations thereof A fineparticle surrounded by thin insulation layer receives electrons from anexternal electrode by the tunnel effect. Because the particle has acapacitance C with respect to the outside, electrostatic energy of theparticle changes by e² /2C when an electron enters therein. Thisprohibits subsequent electron from entering the fine particle by thetunnel effect. Therefore, in order to fabricate the device utilizing thesingle-electron tunnel effect, it is inevitable to arrange quantum dotson an insulator, the quantum dots being formed from microscopic metalparticles having electrostatic energy higher than energy ΔE(approximately 25 mV) required for thermal excitation of electron atroom temperature. In case e² /2C has a low value, it is inevitable tomake an array of quantum dots having energy just above the Fermi levelof microscopic dot higher than the thermal excitation level of electron.Although single-electron operation is lost in this case, transistoroperation can still be achieved. Also microscopic lead wires must beformed even when a quantum device can be achieved, because the tunneleffect does not occur with wide lead wires of the conventional circuitsdue to parasitic capacitance accompanying the lead wires.

As a single-electron memory, such a prototype device was made as a fineline (100 nm wide) of polycrystal Si film having an extremely smallthickness of 3.4 nm and a gate electrode (100 nm) cross each other viaan oxide film gate of 150 nm by depositing a-Si in depressurized CVDprocess and crystallizing at 750° C. (Japanese Journal of AppliedPhysics:

Vol.63, No.12, pp.1248, 1994). This device operates at a roomtemperature and has a potential for the use as an nonvolatile memorywhich operates at a speed exceeding the limitation of the conventionalflash memory. Also an aluminum-based single-electron transistor havingan island electrode measuring 20 nm was fabricated by means of electronbeam lithography and triangular shadow evaporation technologies (Jpn. J.Appl. Phys., Vol.35, 1996, pp. L1465-L1467). This single-electrontransistor has advantages which are not found in silicon-based devices,for example, such as periodical gate modulation characteristic whereinbackground current does not depend on the gate voltage.

However, the single-electron memory based on the polycrystal Si film isunstable because there are variations in the Si film thickness. Also theAl-based single-electron transistor operates at 100 K, far below theroom temperature, and is not of practical use.

SUMMARY OF THE INVENTION

Thus, an object of the present invention is to provide a quantum devicewhich operates stably at the normal temperature and is applicable forcommercial production of single-electron transistor and single-electronmemory.

Another object of the present invention is to provide extremely smalldevices such as diode, transistor and semiconductor light emittingdevices doped with extremely small amounts of impurities, notexperienced in the prior art, by utilizing microscopic dots arranged inthe quantum device.

In order to achieve the above and other objects, the quantum device ofthe present invention is constituted from a two-dimensional array ofquantum dots formed from metal atom aggregates contained inmetalloprotein complex arranged on the surface of a substrate having aninsulation layer at least on the surface thereof with a pitch of thesize of the metalloprotein complex.

The metal which constitutes the metal atom aggregates used in thequantum device is preferably one that can ionize in an aqueous solution.For example, the metal may be iron Fe, aluminum Al, phosphorus P,germanium Ge, zinc Zn, manganese Mn, arsenic As, gold Au, silver Ag,tungsten W or the like, while Fe is preferable.

The diameter of the metal atom aggregates used in the quantum device is7 nm or smaller, preferably 5 nm or smaller, and the pitch of themetalloprotein complex is preferably from 11 to 14 nm.

In a method appropriate for manufacturing the quantum device of thepresent invention, first the metalloprotein complex is let be adsorbedonto a denatured protein membrane, polypeptide membrane or LB membranedeveloped on the surface of an aqueous solution. The membrane is thenplaced on a substrate which is durable to temperatures beyond theburn-out temperature of the protein and has an insulating property onthe surface thereof, to burn out the protein component in a gasatmosphere which does not react with the substrate. The metalloproteincomplex is turned into a metal oxide and remains on the substrate in apattern of dots spaced by a pitch of the size of the protein molecule.Then the metal oxide is heated in a reducing atmosphere to be reduced.The metal oxide is thus reduced into metal atom aggregates which arearranged in a two-dimensional array on the substrate.

The metalloprotein complex used in the quantum device of the presentinvention is preferably ferritin, but the protein may also be onederived from phage or virus.

As the substrate used in the quantum device of the present invention,silicon substrate has wide applicability but glass substrate or ceramicsubstrate may also be used.

A single-electron transistor of the present invention is constitutedfrom quantum dots which are formed from metal atom aggregates containedin metalloprotein complex and arrayed in two-dimensional configurationwith a pitch of the size of the metalloprotein complex on the surface ofa substrate which is durable to temperatures beyond the burn-outtemperatures of the protein and has an insulation layer on the surfacethereof, and comprises a quantum well made of first quantum dot, anelectrode section made from at least three quantum dots located aroundthe quantum well and a wiring section which connects the quantum dotsother than those around the quantum well and the electrode section,wherein the electrode section has a source and a drain comprising secondquantum dots and third quantum dots, respectively, which oppose eachother, and a control gate comprising fourth quantum dots that remain.

The metal used in the metal atom aggregates, the metalloprotein complexand the substrate of the single-electron transistor may be the same asthose used in the quantum device described above.

The diameter of the metal atom aggregate used in the single-electrontransistor is 7 nm or smaller, or preferably 5 nm or smaller, whichmeans that one aggregate normally comprises several thousands of atoms,depending on the metal element. As a consequence, the transition levelnearest to the Fermi level of the aggregate is higher than the thermalexcitation level of electron at room temperature. The quantum well andthe electrode section are separated by a distance of 11 to 14 nm whichallows the tunnel effect to occur. Therefore, the tunnel effect can beobserved in the single-electron transistor at the room temperature or ataround the temperature of liquid nitrogen.

An appropriate method for manufacturing the quantum transistor of thepresent invention comprises, in addition to the steps of manufacturingthe quantum device described above, a step of irradiating the metal atomaggregates with electron beam of a scanning electron microscope, ofwhich beam width is set to be not greater than the pitch, in vacuum inthe presence of a trace of carbon compound, while scanning the electronbeam to have carbon vapor-deposited between the metal atom aggregatesthereby forming lead wires. This causes the source and the drain to beconnected with the quantum dots other than those around the quantum wellby carbon wires. The source of carbon supply may be the residual gasconsisting mainly of hydrocarbons coming from vacuum pump oil. Thiswiring method, which makes it possible to make extremely fine wiresspaced by a distance of the order of nanometers, is best suited to themanufacture of microscopic devices such as single-electron transistor.

A diode of the present invention has quantum dots formed from metal atomaggregates wherein donor impurities and acceptor impurities formed frommetal atom aggregates contained in metalloprotein complex hetero-dimerare arrayed with a pitch of the size of the metalloprotein complex onthe surface of a substrate having an insulation layer on the surfacethereof, and has an n-type region, a p-type region and a pn junctionformed by diffusing the donor impurities and the acceptor impurities viathe insulation layer into the substrate, an electrode section formed ina specified configuration and a wiring section which connects the n-typeregion, the p-type region and the electrode section.

An appropriate method of fabricating the diode of the present inventioncomprises the step of arraying donor impurities and acceptor impuritieswith a pitch of the size of the metalloprotein complex on the surface ofthe substrate, comprising the steps of (a) fabricating a metalloproteincomplex hetero-dimer which includes the donor impurities and theacceptor impurities formed from metal atom aggregates; (b)adsorbing ametalloprotein complex hetero-dimer onto an LB membrane developed on thesurface of an aqueous solution; (c) placing the LB membrane having themetalloprotein complex hetero-dimer adsorbed thereon on a substratewhich is durable to temperatures beyond the burnout temperature of theprotein and has an insulation layer on the surface thereof, and burningout the protein through heat treatment in an inert gas that does notreact with the substrate; and (d) reducing in a reducing atmospherethereby to obtain metal atom aggregates; and (e) forming the n-typeregion, the p-type region and the pn junction by diffusing the donorimpurities and the acceptor impurities via the insulation layer into thesubstrate by heat treatment; (f) forming the electrode section bypatterning electrodes of a specified configuration; and (g) irradiatingthe n-type region, the p-type region and the electrode section withelectron beam of a scanning electron microscope, of which beam width isset to be not greater than the pitch, in vacuum in the presence of atrace of carbon compound, while scanning the electron beam to havecarbon vapor-deposited between the n-type region and the electrodesection, and between the p-type region and the electrode section,thereby forming lead wires.

A transistor of the present invention has quantum dots comprising metalatom aggregates and donor impurities or acceptor impurities formed frommetal atom aggregates contained in metalloprotein complex hetero-trimerwhich are arrayed with a pitch of the size of the metalloproteincomplex, while a group of impurities capable of forming npn structureformed from acceptor impurities having donor impurities on both sidesthereof or a group of impurities capable of forming pnp structure formedfrom donor impurities having acceptor impurities on both sides thereofis arranged on the surface of the substrate, so that the n-type region,the p-type region and the pn junction formed by diffusing the donorimpurities and the acceptor impurities via the insulation layer into thesubstrate, the electrode section formed in a specified configuration,and the wiring section connecting the n-type region, the p-type regionand the electrode section are provided.

A manufacturing method appropriate for the transistor of the presentinvention comprises the step of arranging donor impurities and acceptorimpurities on the surface of a substrate with a pitch of the size of themetalloprotein complex, comprising the steps of (a) fabricatingmetalloprotein complex hetero-trimer by holding the acceptor impuritiesor the donor impurities on both sides of the donor impurity and theacceptor impurity formed from metal atom aggregates; (b) adsorbing ametalloprotein complex hetero-trimer onto an LB membrane developed onthe surface of an aqueous solution; (c) placing the LB membrane havingthe metalloprotein complex hetero-trimer adsorbed thereon on a substratewhich is durable to temperatures beyond the burn-out temperature of theprotein; (d) burning out the protein through heat treatment in an inertgas that does not react with the substrate; and (e) reducing themetalloprotein complex in a reducing atmosphere, and (f) forming then-type region, the p-type region and the pn junction by diffusing thedonor impurities and the acceptor impurities via the insulation layerinto the substrate by heat treatment; (g) forming an electrode sectionof a specified configuration; and (h) irradiating the n-type region, thep-type region, the pn junction and the electrode section with electronbeam of a scanning electron microscope, of which beam width is set to benot greater than the pitch, in vacuum in the presence of a trace ofcarbon compound, while scanning the electron beam to have carbonvapor-deposited between the n-type region and the electrode section, andbetween the p-type region and the electrode section, thereby forminglead wires.

The metal used in the metal atom aggregates, the metalloprotein complexand the substrate of the diode and the transistor may be the same asthose used in the quantum device described above, and the diameter ofthe metal atom aggregate is similarly 7 nm or smaller, or preferably 5nm or smaller.

The manufacturing method appropriate for the diode and the transistor isdifferent from the manufacturing method for the single-electrontransistor, in that two or three kinds of metalloprotein complex ofdifferent metal elements are combined and adsorbed onto the substrate inthe form of hetero-dimer or hetero-trimer, and that the donor impuritiesand the acceptor impurities are diffused by heating to a temperaturefrom 1000 to 1200° C.

The diode and the transistor thus obtained measure about 10 nm by 30 nm,and is expected to operate at an extremely high speed.

A transistor array of the present invention comprises transistorsarranged in a two-dimensional array at intervals of an integer numbertimes the pitch, which is from 11 to 14 nm, wherein quantum dotscomprise metal atom aggregates contained in metalloprotein complexhetero-trimer having at least one layer of apoprotein in the surroundingthereof with donor impurities or acceptor impurities formed from metalatom aggregates being arranged with a pitch of the size of themetalloprotein complex, while a group of impurities capable of formingnpn structure formed from acceptor impurities having donor impurities onboth sides thereof or a group of impurities capable of forming pnpstructure formed from donor impurities having acceptor impurities onboth sides thereof is arranged on the surface of the substrate, thetransistor having an n-type region, a p-type region and a pn junctionformed by diffusing the donor impurities and the acceptor impurities viaan insulation layer into the substrate, an electrode section formed in aspecified configuration and a wiring section for connecting the n-typeregion, the p-type region and the electrode section.

A manufacturing method appropriate for the transistor array of thepresent invention is basically similar to that of the method ofmanufacturing the transistor described above, although different in thatthe hetero-trimer is adsorbed onto the substrate while being surroundedby a multitude of protein molecules which do not include metals, forexample a multitude of apoferritin molecules. Both the proteincomprising metalloprotein complex and the protein such as apoferritinare burned out. Finally, the acceptor impurities and the donorimpurities are arranged at a pitch of the size of the protein, while agroup of impurities and a group of other impurities originating from onehetero-trimer are arranged at intervals an integer n times the size ofthe protein which is from 11 to 14 nm. The integer n can be controlledin terms of the number of protein layers which surround thehetero-trimer.

Because the transistor array of the present invention has transistorsarranged at intervals of the order of nanometers, around ten billiontransistors per square centimeter can be packaged on a chip, making itpossible to achieve an amplifier of high gain.

The manufacturing method appropriate for microscopic dots of the orderof nanometers having quantum effects, comprises the steps of arrangingquantum dots formed from a plurality of metal atom aggregates containedin metalloprotein complex in two-dimensional configuration on a surfaceof a substrate having an insulation layer with a pitch of the size ofsaid metalloprotein complex, and forming column shaped structures on thesurface of said substrate by plasma etching via said masking quantumdots, and insulating a space between said column shaped structures.

A semiconductor light emitting device of the present invention hasp-type and n-type semiconductor layers and an activation layer formed onan insulating substrate, wherein masking quantum dots formed from aplurality of metal atom aggregates contained in metalloprotein complexare arranged in a two-dimensional array on the surface of the activationlayer with a pitch of the size of the metalloprotein complex, andquantum dots formed from the activation layer are formed by plasmaetching via the masking quantum dots.

A manufacturing method appropriate for the semiconductor light emittingdevice of the present invention is different from the method ofmanufacturing the quantum device described above only in that thequantum dots are arrayed on the surface of a light emitting layerlaminated on the insulating substrate, while the step of forming thequantum dots from the activation layer by plasma etching is includedwith the arrayed quantum dots being used as the mask.

The metal contained in the metal atom aggregates, the metalloproteincomplex and the substrate used in the semiconductor light emittingdevice may be the same as those used in the quantum device describedabove, and diameter of the metal atom aggregate is similarly 7 nm orsmaller, or preferably 5 nm or smaller.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome more apparent from the following description of preferredembodiments thereof with reference to the accompanying drawings,throughout which like parts are designated by like reference numerals.

FIG. 1 is a schematic diagram showing the ferritin structure accordingto the present invention.

FIG. 2A is a schematic diagram showing the step of manufacturing thequantum device of the present invention.

FIG. 2B is a schematic diagram showing the step of manufacturing thequantum device of the present invention.

FIG. 2C is a schematic diagram showing the step of manufacturing thequantum device of the present invention.

FIG. 2D is a schematic diagram showing the step of manufacturing thequantum device of the present invention.

FIG. 3 is a schematic sectional view showing the quantum device on thesilicon substrate of the present invention.

FIG. 4 is a microscope (SEM) photograph of 100,000 times magnificationshowing the quantum device on the silicon substrate of the presentinvention.

FIG. 5 is a schematic plan view showing the single-electron transistorformed from the quantum device on the silicon substrate of the presentinvention.

FIG. 6 is a schematic sectional view showing the hetero-dimer of themetalloprotein complex of the present invention.

FIG. 7 is a schematic sectional view showing the structure of the diodeof the present invention.

FIG. 8 is a schematic sectional view showing the structure of thetransistor of the present invention.

FIG. 9 is a schematic sectional view showing the hetero-trimersurrounded by apoferritin of the present invention.

FIG. 10 is a schematic plan view showing the transistor array of thepresent invention.

FIG. 11 is a schematic sectional view showing the structure of thesemiconductor light emitting device of the present invention.

FIG. 12 is a schematic sectional view showing the method of bonding thelead frame member of the semiconductor light emitting device of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This application is based on application No.9-157436 filed May 30, 1997in Japan, the content of which is incorporated hereinto by reference.

Preferred embodiments of the quantum device and the device employing thesame according to the present invention will now be described below withreference to the accompanying drawings.

Embodiment 1

The first embodiment of the present invention is an example of methodfor manufacturing the quantum device. A solution of ferritin isprepared. Ferritin is a metalloprotein complex comprising a core 1 ofFe₂ O₃ enclosed in a shell 2 of protein as shown in FIG. 1, which can beextracted from organs such as spleen and liver of animals such as horseand cow. The core 1 has a diameter about 6 nm, and includes from 1000 to3000 iron atoms. The shell 2 is a trisoctamer of protein having amolecular weight of about 20,000. The trisoctamer measures about 12 nmacross.

As shown in FIG. 2A, a tank 3 made of teflon is filled with a bufferliquid wherein ferritin 4 is dispersed and PBLH membrane (polypeptidemembrane) 5 is spread on the liquid surface. Hydrogen ion concentrationof the liquid is controlled to about pH6 by using a proper acid, forexample hydrochloric acid. Because the PBLH membrane 5 is positivelycharged and the ferritin 4 is negatively charged, ferritin 4 is adsorbedonto the PBLH membrane 5, resulting in a two-dimensional crystal beingformed (FIG. 2B). Then after having a silicon substrate 6, which isabout 500 μm thick and is oxidized deep into the surface to have the2-dimensional crystal deposited on the substrate (FIG. 2C), thesubstrate is taken out of the tank 3 (FIG. 2D). The substrate is thenheat-treated in an inert gas which does not react with the silicon, forexample nitrogen, at a temperature of 500° C.

Protein and the PBLH membrane are burned out, leaving Fe₂ O₃ or otheriron oxide 8 arranged two-dimensionally via a thin film 7 of siliconoxide on the substrate, as shown in cross sectional view of FIG. 3. Thatthe iron oxide 8 is arranged two-dimensionally is confirmed throughmeasurement by AFM analysis which shows the iron oxide 8 has only twoheights, 5.3 nm and 10.6 nm, and mostly 5.3 nm. SEM photograph(×100,000) of two-dimensional crystal of iron oxide obtained after onehour of eat treatment in nitrogen atmosphere at 500° C. In FIG. 4, manywhite dots represent the iron oxide and black portions in thesurrounding thereof are protein and silicon that remain. When thetwo-dimensional crystal is subjected to heat treatment again for 60minutes in a hydrogen atmosphere at 800 to 500° C., a quantum device isobtained comprising a multitude of iron atom aggregates arrangedtwo-dimensionally on the oxide film of the surface of the siliconsubstrate 6. The diameter of the aggregate is about 6 nm, the same asthat of the core of iron oxide contained in ferritin, and the pitchbetween aggregates is about 12 nm, the same as one side of the proteinshell of ferritin. As shown in the plan view of FIG. 5, asingle-electron transistor is obtained by using one of the aggregates Mas a quantum well Q, at least three quantum dots surrounding the quantumwell as an electrode, second and third quantum dots which oppose eachother interposing the quantum well as a drain D and a sources,respectively, remaining fourth quantum dot in the surrounding as a gateG, and other aggregates M as wiring.

Because the quantum well Q of the single-electron transistor is anaggregate comprising one thousand to three thousand atoms, thetransition level nearest to the Fermi level of the quantum well ishigher than the thermal excitation level of electrons at roomtemperature. The quantum well Q, the drain D and the source S areseparated by a distance of 12 nm which allows the tunnel effect tooccur. Therefore, tunnel effect can be observed in the single-electrontransistor at the room temperature or at a practically feasibletemperature.

Embodiment 2

This embodiment is an example of wiring method for the quantum deviceobtained in the first embodiment. The quantum device obtained in thefirst embodiment is put in the chamber of a field emission scanningelectron microscope (FE-SEW, inside of the chamber being pumped vacuumto about 10⁻⁶ Pa. Electron beam with a width being set to about 5 nm isscanned between the drain D, the source S or the gate G and one or moreof the iron atom aggregates M1 through M3. This results in a lead wiremade of carbon 20 nm wide connecting the drain the source, the gate andthe iron atom aggregates M1 through M3 and electrodes M1 through M3being formed.

Embodiment 3

The third embodiment is an example of the diode of the presentinvention. A column filled with polystyrene beads of mean diameter 100μm having ammonium radical NH⁴⁺ bonded onto the surface thereof isprepared. Aluminum oxide is put in the position of an apoferritin core,and metal-apoferritin complex thus obtained is passed through the columnto be adsorbed onto the polystyrene beads. Then phosphoric acid is putin the position of another apoferritin core, and metal-apoferritincomplex thus obtained is passed through the same column to be adsorbedonto the polystyrene beads. The two kinds of metal-apoferritin complexare made to bond by disulfide linkage between sulfur atoms of a cysteineresidue of protein, thereby fabricating a hetero-dimer shown in FIG. 6.The hetero-dimer is let flow out of the column into the same tank asthat of the first embodiment.

Under the same conditions as those of the first embodiment except thatthe ferritin of the first embodiment is replaced with the hetero-dimer,the two-dimensional crystal is made to deposit on the silicon substrate,protein is burned out and reduced into metal atom aggregate. Aluminumatom aggregate and phosphorus atom aggregate are arranged with a space a12 nm between the centers thereof on the silicon substrate. This issubjected to heat treatment under the same conditions as those of thefirst embodiment so that the aluminum atom aggregate and phosphorus atomaggregate are arranged on the silicon substrate, which are subjected toheat treatment at a higher temperature so that the aggregates arediffused into the silicon substrate right below to form n- and p-typesemiconductors. Then Al film is formed into a specified configuration bymeans of photolithography technology or electron beam lithographytechnology while masking the n- and p-type semiconductors and formed anelectrode section. The diode is formed by forming a carbon wiresimilarly to the second embodiment 2 (FIG. 7). The diode measures 10 nmby 20 nm.

Embodiment 4

The fourth embodiment is an example of the transistor of the presentinvention. Hetero-dimer is fabricated in a column in the same procedureas that of the third embodiment. Aluminum oxide is put in the positionof third apoferritin core, and metal-apoferritin complex thus obtainedis passed through the same column to be adsorbed onto the polystyrenebeads. Then the hetero-dimer and the metal-apoferritin complex are madeto bond by disulfide linkage between sulfur atoms of a cysteine residueof protein, thereby fabricating a hetero-trimer. The hetero-trimer islet flow out of the column into the same tank as that of the firstembodiment.

Under the same conditions as those of the first embodiment except thatthe ferritin of the first embodiment is replaced with the hetero-trimer,the two-dimensional crystal is made to deposit on the silicon substrate,protein is burned out and reduced into metal atom aggregate. Aluminumatom aggregate and phosphorus atom aggregate are arranged with a spaceof 12 nm between the centers thereof on the silicon substrate. This issubjected to heat treatment under the same conditions as those of thesecond embodiment so that the aluminum atom aggregate and the phosphorusatom aggregate are diffused into the silicon substrate right below toform p-, n- and p-type semiconductors. Then an electrode section 3 and acarbon wire are formed similarly to the third embodiment (FIG. 8). Thetransistor measures 10 nm by 30 nm.

Embodiment 5

The fifth embodiment is an example of the transistor array of thepresent invention. Hetero-trimer is fabricated in a column in the sameprocess as that of the fourth embodiment. A large amount of apoferritinis passed through the same column to be adsorbed onto the polystyrenebeads. Then the hetero-trimer and the apoferritin are made to bond bydisulfide linkage between sulfur atoms of a cysteine residue of protein,thereby surrounding the hetero-trimer with a layer comprising amultitude of apoferritin as shown in FIG. 9.

Under the same conditions as those of the first embodiment except thatthe ferritin of the first embodiment is replaced with the hetero-trimersurrounded by the apoferritin, the two-dimensional crystal is made todeposit on the silicon substrate, protein is burned out and reduced intometal atom aggregate. Aluminum atom aggregate and phosphorus atomaggregate are found to be arranged with a space of 12 nm between thecenters thereof on the silicon substrate. This is subjected to anotherheat treatment under the same conditions as those of the firstembodiment so that the aluminum atom aggregate and the phosphorus atomaggregate are arranged on the silicon substrate, which are furthersubjected to heat treatment at a higher temperature and are diffusedinto the silicon substrate right below to form n- and p-typesemiconductors. These semiconductors function as transistor array, eachmeasuring 10 nm by 30 nm.

Embodiment 6

The sixth embodiment is an example of the semiconductor light emittingdevice of the present invention which will be described below withreference to FIG. 11. A single crystal sapphire substrate 101 havingbeen cleaned with an organic solvent and heat treatment is set on asusceptor which is put in a reaction chamber of an MOCVD apparatus.(formation of a buffer layer on a sapphire substrate)

While circulating hydrogen gas through the reaction chamber at normalpressure, the sapphire substrate is etched in gas phase at 1100° C. Thenwith the temperature being lowered to 400° C., hydrogen gas, ammonia gasand trimethyl aluminum gas are supplied in predetermined proportions,thereby to form a buffer layer 102 comprising AlN.

(Formation of an n-type GaN layer of silicon layer doped with silicon)

With the sapphire substrate 1 maintained at 1150° C., hydrogen gas,ammonia gas, trimethyl aluminum gas and silane gas are supplied inspecified proportions, thereby to form a silicon-doped n-type GaN layer103.

(Formation of an n-type AlGaN clad layer)

With the sapphire substrate 1 maintained at 1150° C., hydrogen gas,ammonia gas, trimethyl gallium gas, trimethyl aluminum gas and silanegas are supplied in specified proportions, thereby to form asilicon-doped n-type AlGaN clad layer 104.

(Formation of light emitting InGaN layer on n-type AlGaN)

With the sapphire substrate 1 maintained at 800° C., hydrogen gas,ammonia gas, trimethyl gallium gas and trimethyl indium gas and silanegas are supplied in specified proportions, thereby to form an InGaNlayer 105.

(Formation of two-dimensional crystal membrane on InGaN layer)

A substrate having the InGaN layer as the top layer thereof is floatedin a tank wherein a two-dimensional crystal is formed, similarly to thesilicon substrate of the first embodiment, and the substrate with thetwo-dimensional crystal membrane deposited thereon is taken out of thetank. Then the substrate is subjected to heat treatment in an inert gasat 500° C., so that dots of iron oxide 106 are arranged regularly on theInGaN layer 105 at specified intervals.

(Formation of quantum dots of InGaN layer)

The substrate having the dots of iron oxide 106 arranged regularlythereon is subjected to plasma etching by electron cyclotron resonanceabsorption (ECR), under conditions of introducing SF₆ as plasma gas,pressure of about 10⁻² Pa, with microwave applied so that plasma isgenerated by electron cyclotron resonance absorption. At this time, thesubstrate is maintained at a low temperature to prevent chemical etchingfrom taking place. While the temperature is preferably -50° C. or lower,it is necessary to determine the optimum temperature taking variousinfluences into consideration and precisely control the substratetemperature, in order to maintain the influence of the plasma state dueto the substrate cooling efficiency and vacuum vessel. Through theplasma etching, the iron oxide dots become mask thereby forming circularcolumn structures several nanometers in diameter arranged regularly.Quantum dots are formed by filling the space between the circular columnstructures with an insulating material such as oxide.

(Formation of a p-type AlGaN layer on quantum dot)

With a sapphire substrate 101 maintained at 1050° C., hydrogen gas,ammonia gas, trimethyl gallium gas, trimethyl aluminum andcyclopentadienyl magnesium are supplied in specified proportions,thereby to form a magnesium-doped p-type AlGaN clad layer 107.

(Formation of a p-type GaN layer on p-type AlGaN layer)

With the sapphire substrate 101 maintained at 1050° C., hydrogen gas,ammonia gas, trimethyl gallium gas, trimethyl aluminum andcyclopentadienyl magnesium are supplied in predetermined proportions,thereby to form a magnesium-doped p-type GaN contact layer 108.

(Formation of electrode)

In a tank maintained at high degree of vacuum, an Ni layer isvapor-deposited on the top surface of the specimen described above, andthe Ni layer is formed into a specified configuration byphotolithography thereby to form an electrode 109 of p-type GaN. On theother hand, the specimen is etched on the p-type GaN side to expose then-type GaN layer, and Al layer is vapor-deposited on part of the exposedn-type GaN thereby to form an electrode 110 of n-type GaN.

(Separation of device)

The wafer formed as described above is cut to a specified size and theelectrodes are bonded onto leads 111, 112 of a lead frame thereby toform light emitting devices (FIG. 12).

In the prior art, quantum dots have been formed in the light emittinglayer by utilizing the capability of InGaN of the light emitting layerto spontaneously forming quantum dot, but uniform quantum dots cannot beformed. According to the present invention, because of plasma etchingemploying two-dimensionally arranged dots of iron oxide contained inferritin as the mask, quantum dots of uniform sizes of nanometer ordercan be formed, thereby making it possible to improve the internalquantum efficiency and improve the efficiency of emitting blue light.

The quantum device of the present invention has, because microscopicmetal atom aggregates are arranged at extremely small intervals andmicroscopic lead wires can be made by the wiring method of the presentinvention, application for single-electron transistor, single-electronmemory, diode, transistor and semiconductor light emitting device whichoperate stably at the normal temperature.

What is claimed is:
 1. A method of fabricating single-electrontransistor comprising quantum dots formed from microscopic metalparticles of which transition level nearest to the Fermi level is higherthan the thermal excitation level of electron at room temperature, saidmethod comprising the steps of:(a) adsorbing a metalloprotein complexonto an LB membrane developed on a surface of an aqueous solution; (b)placing said LB membrane having said metalloprotein complex adsorbedthereon on a substrate which is durable to temperatures beyond theburn-out temperature of said protein and having an insulation layer atleast on the surface thereof; (c) burning out said protein through heattreatment in an inert gas that does not react with said substrate; and(d) reducing said metalloprotein complex thereby to obtain metal atomaggregates; and (e) irradiating said metal atom aggregates with electronbeam of a scanning electron microscope, of which beam width is set to benot greater than said pitch, in vacuum in the presence of a trace ofcarbon compound, while scanning said electron beam to have carbonvapor-deposited between said metal atom aggregates thereby forming leadwires.
 2. The method according to claim 1, further comprising the stepof adsorbing ferritin as said metalloprotein complex onto an LB membranedeveloped on the surface of an aqueous solution.